Periodic Table

CHAPTER 4 PERIODIC TABLE OF ELEMENTS

• Elements are arranged in an increasing order of proton number • Group – vertical column (Group 1 to Group 18) • Period – horizontal column (Period 1 to Period 7)

• No. of valence electrons shows the group of an element • 1 and 2 valence electrons = Group 1 and Group 2 • 3 to 8 valence electrons = Group (10 + no. of valence electrons) = Group 13, 14, 15, 16, 17, 18

• The period number of an element = the number of shells filled with electrons

• An atom of element X has a proton number of 15. In which group and period can we find element X in the Periodic Table?

• Number of electrons = Number of protons = 15 • The electron arrangement = 2.8.5 • Atom X has 5 valence electrons → Group 15 • Atom X has 3 shells filled with electrons → Period 3

NOBLE GASES Helium Neon Argon Krypton Xenon Radon

Noble Gases

INERT

MONOATOMIC

WHY?

Achieve a stable electron arrangement

USES OF NOBLE GASES

USES OF NOBLE GASES

USES OF NOBLE GASES

USES OF NOBLE GASES

USES OF NOBLE GASES

USES OF NOBLE GASES

PHYSICAL PROPERTIES OF GROUP 1 ELEMENTS

Hardness and density increase.

Atomic size increases

Melting and boiling points decrease.

PHYSICAL PROPERTIES OF GROUP 1 ELEMENTS

• Soft

metals

• Low melting and boiling points • Silvery and shiny surface • Good conductors of heat and electricity

Lithium burns slowly with a red flame. A white solid is produced.

4Li + O2 → 2Li2O

Sodium burns brightly with a yellow flame. A white solid is produced.

4Na + O2 → 2Na2O

Potassium burns very brightly with a purple flame. A white solid is produced.

4K + O2 → 2K2O

Li2O + H2O → 2LiOH

Na2O + H2O → 2NaOH

Na2O + H2O → 2NaOH

WHY?

Have same number of valence electron, that is 1

Valence electrons

Exist as DIATOMIC MOLECULE

2

2

2

2

2

Chloride ion, Cl-

• The period number represents the number of shells filled with electrons in an atom

All the atoms have 3 shells filled with electrons Proton number increases from left to right

Atomic size DECREASES Electronegativity INCREASES WHY?